1. Technical Field
The present invention relates to a laser machining method for cutting an unnecessary part of a resin sheet adhering to a substrate.
2. Related Art
In recent years, printed wiring hoards or glass substrates having circuits disposed thereon (hereinafter generally referred to as substrate(s)) have been covered with adhesive resin films for protecting the substrates from damage and/or contamination.
The resin film used is slightly larger than the substrate, and the part of the resin film that extends beyond the sides of the substrate is cut by a laser machining apparatus as illustrated in FIG. 7. A workpiece 6 is a substrate 61 having a resin film 62 adhered thereto as illustrated in FIG. 8. The resin film is cut along the outline of the substrate 61. The workpiece 6 is mounted and secured on an X-Y table 7. Therefore, the workpiece 6 is moved with the X-Y table 7 which is driven by a table driving unit. Here, the speed of the X-Y table 7 is detected by using an X-axis scale 9 and a Y-axis scale 10. A laser source control unit 2 controls a laser source 1 and also an AOM control unit 4 for an acousto-optic modulator 3 (hereinafter referred to as AOM) by feeding a signal S1. The AOM control unit 4 controls the AOM 3 by communicating (S3, S4) with a movement detection unit 11 for detecting a predetermined amount of movement. Upon the reception of the signal S1 from the laser source control unit 2, the laser source 1, which is a continuous wave (CW) carbon dioxide laser, emits a continuous wave (CW) laser beam L1. The CW laser beam L1 is modulated into a pulsed beam L2 using the AOM 3 as a high-speed chopper, and then is converged on the workpiece 6 through an optical system 5. With this beam, the resin film 62 is cut by relative movement between the laser beam L2 and the workpiece 6. These laser source control unit 2 and table drive unit 8 are controlled by a control unit (not shown) storing a machining program.
In such machining, it is well known the laser pulses can be stabilized by slicing a continuous wave laser beam or a quasi-continuous wave laser beam using an AOM, as described in the paragraph [0010] of JP-A-2006-101764 and the paragraph [0035] of JP-A-2013-063169, for example. Where, the quasi-continuous wave laser beam (hereinafter also referred to as “quasi-CW laser beam”) is obtained by increasing the duration of pulsed radiofrequency (RE) discharge for laser oscillation to 80% or more.
It is also known that the pitch of holes machined with the laser pulse spots is controlled by adjusting the intervals between successive laser pulses (hereinafter referred to as “laser pulse interval(s)” or simply “pulse interval(s)”) in accordance with the moving speed of the workpiece as described in the paragraph [0009] of JP-A-200-101764.
In the case of cutting the resin film 62 along the outline of the substrate 61 having corners (arcuated portions) 64 and straight lines as illustrated in FIG. 8, the speed of machining is high and constant along the straight lines 63, (herein after referred to as High Speed period) and decreased by deceleration just before the corners 64 (herein after referred to as Decelerating period) and is low and constant along the corners 64 (herein after referred to as Low Speed period); then, after the corners 64, the speed is increased by acceleration (herein after referred to as Accelerating period) to return to its constant value from the initial High Speed period.
FIG. 9A (on the upper side) is a conceptual timing diagram show relationship between a conventional laser pulse train and a speed change of the X-Y table. FIG. 9B (on the lower side) is a schematic diagram of a locus of laser spots in accordance with the laser pulses described in FIG. 9A. The pulse intervals are gradually increased, such as t1<t2′<t3′<t4′ in FIG. 9A, when the speed of the X-Y table is decreased (Decelerating period), and is adjusted to an interval in accordance with a low speed in the Low Speed period (corner 64). On the contrary, when the speed of the X-Y table is increased (Accelerating period), the pulse intervals are gradually decreased in reverse order to the Decelerating period, and then returns to the pulse interval in the High Speed period. As described above, the intervals along the locus of the laser spots is kept constant.
In the machining as described above, the straight lines 63 are cut without any problem. The machining may be insufficient, however, in the corners 64 (including just before and just after) where the speed of the X-Y table has to be decreased.
An object of the present invention is to solve the problem in machining the portion where the speed of the X-Y table has to be decreased.